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Full text of "Flora Indica Vol-I"

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170                                     FLORA  INDTCA.
.between the valley that ascends from one river, to the cor-
responding valley ihat descends to the other river, can only
be detected by the observation of the drainage; whence the
two valleys appear to form one. Such is the case with the
Dehra Dhiin, which appears to form one continuous trans-
verse valley between the Jumna and the Ganges, but which
really consists of two valleys; one descending from the vil-
lage of Dehra (which occupies the col) westerly to the Jumna,
and the other descending from the same spot easterly to the
Ganges. Other Dhuns, again, are simply very broad, open
valleys, differing in no physical features from those that occur
in -other parts of the mountains. In the Panjab-IIimalaya,
where the tertiary sandstones acquire a great development,
two or three such valleys occur in succession before the
higher mountains begin. These valleys, or Dhiiris, arc not/as
is very generally supposed, continuous along the whole ex-
tent of the Himalaya, and interposed between the tertiary
and secondary mountains. They are merely the outer scries
of lateral valleys, and are always of limited extent.
In the enormous chain of the Himalaya, which rises nearly
from the level of the sŤa to perpetual snow, we have of course
every variation of temperature between tropical or subtropical
heat and extreme cold. The diminution of temperature is 1°
for 300 feet of elevation in the more humid, and for 400 feet
in the drier part of the chain. The elevation of the Bow-
line, at equal distances from the plains, is nearly uniform
throughout the whole extent of the chain, the increase of
latitude of the more westerly part being compensated for by
the greater distance from- the sea, and consequent diminished
snow-fall This level on the outer ranges has been deter-
mined to be about 16,000 feet, Imt it becomes higher ou the
inner ranges, and in the Tibetan Himalaya is not under 19
or 20,000 feet.
The climate of the Himalaya varies much in different parts.
During the winter season the weather is generally unsettled;
for while the worth-cast monsoon is Wowing over the lower